Machining apparatus and method to machine surfaces in recesses of workpieces

ABSTRACT

In a machining apparatus to machine surfaces in recesses of workpieces, especially tools with flutes and cutting edges, such as twist drills, milling heads, reamers, and similar, the machining apparatus has a circular disk-shaped or frustum-shaped machining body with a symmetrical and rotational axis which is seated in a bearing in a rotatable manner and is connected with a machining drive to generate a rotational movement of the machining body about its rotational axis. The machining body has magnets acting outward in relation to the rotational axis to retain magnetic or magnetizable, abrasive machining powder on a circumferential surface of the machining body. A workpiece holder positionable relative to the machining body and moveably driven at least in an advancing or rotational direction or both is connected at least indirectly by means of a corresponding positioning medium and drives to the bearing of the machining body.

BACKGROUND

The preferred embodiment relates to a machining apparatus for machining surfaces in recesses of workpieces. In particular, the machining apparatus serves to machine workpieces with flutes and cutting edges, such as twist drills, milling heads, reamers and similar. The machining apparatus has a machining body that is constructed about a rotational axis in a rotation-symmetric manner. To generate a rotational movement about its rotational axis, the machining body is rotatably positioned on the one hand and connected to a machining drive on the other. The machining body is constructed as a magnetic head that has a plurality of magnets to retain a magnetic or magnetizable, abrasive machining powder. In addition, the preferred embodiment relates to a method for de-burring and polishing surfaces of groove-shaped recesses of workpieces, in particular cutting tools with flutes.

Specifically the de-burring of cutting edges and the polishing of grooves of such cutting tools are significant since such grooves serve to transport media such as coolants for screw-type compressors or the carrying-away of machining chips for cutting tools. Complete removal of residual burrs subsequent to the groove's manufacturing process as well as a reduction of the surface roughness decrease flow resistance or reduce friction. This results in improved efficiency or an increase in the service life of the workpieces or tools possessing grooves.

Known devices to de-burr and polish the flutes of cutting tools for example are brush machines. However, the machining of workpieces and tools with brush machines often and necessarily results in the uncontrolled and undesired rounding off of cutting edges. This is related to the fact that a part of the abrasive brush hairs of a brush cluster are pressed against the cutting edge. Rigid specifications pertaining to a precise geometry of the cutting edge cannot be fulfilled in the case of machining with a brush machine. Another disadvantage of such brush machines is that the brushes wear in such a manner that the brushes must be regularly replaced in a costly manner.

As an alternative to brushing, a jet procedure is known for the de-burring of edges, whereby a high-pressure jet of fluid, such as water, is generated. An abrasive effect of the jet can be strengthened by mixing in abrasive materials of a particular grain-size. Such a jet procedure has the disadvantage that the expenses of generating the jet and reprocessing the material required for the jet are high. An additional disadvantage is that the workpieces must be treated in a sealed container. This prevents the automatic supply and removal of workpieces. For a laminar finish, for example the finish of a flute, the jet must be guided to this surface by means of additional movements of the jet nozzle or multiple jet nozzles must be provided and oriented precisely amongst each other. In both cases, the device-related 2expenses are considerable, especially when tools and workpieces of various geometries must be machined using one system.

Another alternative to this known method is a magnet-abrasive grinding method known from WO02/38334. WO02/38334 describes a machining device with a machining body that is capable of binding a magnetizable, abrasive grinding powder as machining powder by means of a plurality of permanent magnets and pole shoes and to guide it over a surface to be machined. In the device known from WO02/38334, the magnetizable grinding powder is retained by the machining body by means of magnetic force, but due to its coating thickness, it behaves like an elastic tool that acts upon the surface to be machined. In doing so, the force exerted by the machining powder on the respective workpiece surface can be adjusted by means of the distance between the workpiece surface and the magnets retaining the machining powder. In addition, the intensity of the cutting exercised on the workpiece by the machining powder can also be adjusted by the magnitude of the relative movement between the magnets and the surface to be machined.

SUMMARY

It is an object to create a machining apparatus that permits the machining of recesses, such as grooves of workpieces or tools, whereby the disadvantages of the prior art should be preferably avoided.

A machining apparatus is provided to machine a surface in a recess of a workpiece. A circular disk-shaped or frustrum-shaped machining body is provided with a symmetrical and rotational axis which is rotatably seated in a bearing and is connected to a machining drive to generate a rotational motion of a machining body about said rotational axis. The machining body has magnets acting outwardly in relation to the rotational axis to retain magnetic or magnetizable abrasive machining powder on a circumferential surface of the machining body. A workpiece holder is provided for said workpiece positionable relative to the machining body and moveably driven in an advancing or rotation direction or both and which is at least indirectly connected to the bearing of the machining body by means of corresponding positioning media and drives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic drawing of a rotation-symmetric machining body with a circumferential frustum-shaped edge along with a view of a workpiece, in the form of a twist drill, to be machined;

FIG. 2 depicts a robot-controlled tool whose spiral flute is polished by a method of the preferred embodiment; and

FIG. 3 depicts a machining apparatus to polish the spiral flute of highly magnetic tools.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and/or method, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

According to the preferred embodiment a machining apparatus is provided of a type described in the background, in which a machining body is constructed as a rotation-symmetric magnetic head, whose magnets are arranged in such a manner that they retain the abrasive machining powder on the magnetic body's surface oriented outward in relation to the rotational axis. The apparatus according to the preferred embodiment also has a workpiece holder that can be positioned relative to the machining body and that can be driven in a moveable manner at least in an advancing or rotational direction or both, said holder being connected at least indirectly by means of a corresponding positioning medium and drives to the bearing of the machining body. The workpiece holder allows one to machine recesses in a workpiece, such as flutes of a twist drill, with a single machining body over the entire length of the respective groove.

The preferred embodiment is based upon the knowledge that the machining body known from WO02/38334 is constructed as a cylinder, in which the magnetic field retaining the machining powder is generated on one of the faces, whereby this arrangement is well suited for the machining of flat or convex surfaces, yet not for surfaces in recesses of workpieces. Such recesses, like grooves for example, can only be machined to the effective depth of the magnetic field. This effective depth is limited by the magnetic field strength which decreases with the square of the distance from the magnet surface. In practice, this results in a usable effective depth of 3 mm maximum. However, many workpieces and tools have recesses, such as grooves for example, that are deeper and that can therefore not be machined with the device known from WO02/38334. For the first time, the machining apparatus according to the preferred embodiment allows the machining of twist drills having diameters greater than 12 mm, even though their flutes have a depth that is greater than 3 mm. Thus, the machining apparatus according to the preferred embodiment removes a limitation previously considered as system-intrinsic in the field of utilization.

With this type of machining apparatus and due to the magnetic attractive forces on the machining powder adhering externally to the machining body as well as for corresponding configurations, one can insert the corresponding magnets themselves into the grooves to be machined of a workpiece. The insertion depth of the machining body into the groove is selected in such a manner that the distance between the machining surfaces of the magnetic head and the surfaces to be machined in the groove is less than or equal to 3 mm, whereby a sufficiently great field strength is assured on the surfaces to be machined, which is a prerequisite for the abrasive work of the grinding powder.

In order to be able to machine a groove in its entire length, the respective workpiece is run past the machining body with the help of the corresponding moveable workpiece holder. The guiding of the workpiece occurs preferably in such a way that the local orientation of the helix-like, coiled flute of a twist drill at the machining location matches the respective effective tangents of the machining body at least approximately. This allows the machining of a flute in which the cutting edges are not impaired and permits a preferably deep insertion of the machining body into the flute. If a workpiece, such as a twist drill has several grooves, then these grooves can be machined one at a time sequentially or multiple machining heads can be provided that engage simultaneously with various grooves.

Specifically in relation to the machining of a twist drill's flutes for example, an advantageous machining apparatus is one in which the workpiece holder has a feed drive and a rotation drive with which the workpiece can be simultaneously fed and rotated, whereby the feed drive and rotation drive are connected to a control unit designed in such a way that the workpiece feed and workpiece rotation are inter-coordinated. In reference to the machining of a twist drill, this means that the twist drill is arranged by means of the workpiece holder's positioning medium in such a manner that the tangents of the machining body at the respective machining point run parallel to the longitudinal axis of the flute to be machined. The feed drive allows one to move the workpiece, the twist drill for example, along the workpiece's longitudinal axis. In the case of twist drills with helix-like, coiled flutes, this linear advancing motion must be given a rotational motion of the workpiece that is coordinated with the advancing motion in such a manner that the resulting overall movement corresponds to the pitch of the flute.

The relative motion between the machining body and workpiece thus results from the rotational movement of the machining body and the movement of the workpiece specified by the feed drive or rotation drive or both. The feed drive thereby causes a linear movement of the workpiece, while the rotation drive causes a rotational movement of the workpiece. In the case of those grooves that run parallel to a longitudinal axis of a workpiece, only a linear feed movement is required. To machine other workpieces that have a circumferential, enclosed groove on a surface area, whereby the groove runs in a plane perpendicular to a symmetrical axis of the workpiece, the workpiece holder must only execute one rotational movement effected by the rotation drive in order to machine the groove of the workpiece over the entire circumference of the workpiece. Examples of such workpieces are crankshafts whose bearing points are to be polished between the crank cheeks. In this case, the machining body enters between the crank cheeks until the machining distance to the bearing surface is 3 mm or less. The crankshaft then executes a rotational movement about its longitudinal axis. In doing so, the rotational axis of the machining body is preferentially oriented parallel to the rotational axis of the crankshaft.

As already mentioned, workpieces with a helix-like, coiled groove, such as twist drills for example, require a synchronized movement both in the feed direction (linear movement) and in the rotational direction (rotational movement).

A circular disk shape has proven itself to be a particularly advantageous shaping for the machining body, whereby magnets are arranged on the circumference of the circular disk. In addition, the design of the magnetic head as a frustum is especially advantageous for working on relatively small grooves, whereby a circumferential edge on the cone's base is rounded off and equipped with magnets.

FIG. 1 depicts a rotation-symmetrical machining body 14 with a circumferential frustum-shaped edge 13 of a machining apparatus otherwise not further depicted. The machining body 14, also called a magnetic head, has on its edge a plurality of not further depicted magnets. As can be seen in FIG. 1, the frustum-shaped edge 13 of the machining body 14 is rounded off, so that it approximately copies the form of flute 12 of the twist drill 11 to be machined. A magnetic, abrasive grinding powder not depicted in this figure adheres to the magnets. When the frustum-shaped edge 13 is inserted into flute 12, the remaining space is filled by this grinding powder. A machining drive to drive the machining body 14 about its rotational axis 15 is not further depicted.

The workpiece depicted in FIG. 1 is a twist drill 11, whose flute 12 is to be machined. To do so, the workpiece 11 (the twist drill) is fastened to a workpiece holder that, on the one hand, is to be oriented with the help of a positioning medium, not shown in further detail in this figure, relative to the rotational axis 15 of the machining body 14, and, on the other, is connected to a feed drive and a rotation drive that enable an advancing movement in the longitudinal direction of the workpiece and a rotational movement about a rotational axis of the workpiece.

As can be seen in FIG. 1, the workpiece 11 is arranged in such a manner that a tangent abutting the frustum-shaped edge 13 and the rotational axis of the twist drill 11 to be machined form an angle in such a manner that at the machining location, the edge runs through flute 12 in a collision-free manner. This angle corresponds to the so-called pitch of the twist drill and must be set for each drill-type. The gaps to be set between the edge inserted into the flute and the surface of the flute should preferentially be between 1-2 mm.

To machine the flute 12, the machining body 14 is placed into a rotational motion about the rotational axis 15. This rotational motion has the greatest share of the relative motion between the twist drill 11 and the abrasive machining powder, said motion being required to machine the flute. The machining powder (not depicted in FIG. 1) is retained outside on the edge 13 of the machining body 14 by the magnets of the machining body and pulled along by its rotation. It thereby performs abrasive work in the flute with the objective of reducing roughness.

In order to machine the flute 22 over its entire length, the workpiece holder not depicted in this figure executes during the machining process both an advancing motion along the workpiece's rotational axis as well as a rotational motion around this rotational axis. This linear advancing motion and the rotational motion are synchronized with each other in such a manner that the edge 13 of the machining body 14 along with its tangent always runs approximately centered in flute 12. This means that the advancing motion and the rotational motion of the workpiece are synchronized or coordinated to correspond to the pitch of the flute 12.

Two particularly advantageous apparatuses with which a tool having a spiral-shaped flute can be polished are explained below.

FIG. 2 depicts the implementation of an industrial robot 27 to guide the tool 25 to be machined along the machining edge of a magnetic head 23. The objective is to polish the spiral flute of the cutting tool 25 by means of the magnetic grinding powder adhering to the circumferential edge 24. The grippers 26 of the robot 27 extract from a non-depicted stack the cutting tool 25 to be machined. It may be a milling cutter, a tap, or a drill twist, for example. This tool is positioned on the circumferential machining edge 24 of the rotating magnetic head 23 in the manner already described for FIG. 1. The robot is programmed in such a manner that it executes an advancing motion in the direction of the tip of tool 25, which is synchronized according to the pitch of the tool with a rotational motion of the tool about its rotational axis. In this manner, the entire length of the flute is polished by the powder adhering to the machining edge 24 of the rotating magnetic head 23. The rotating magnetic head 23 is driven by means of a three-phase AC motor 21 and a coupling 22. A dish 29 catches removed chips from the machined tools. The depicted embodiment is especially suited for metal carbide tools. These are only weakly magnetic and therefore the magnetic attractive forces exercised by the magnetic head 23 on the tool and thus the robot's grippers are slight.

FIG. 3 depicts the implementation of the procedure according to the preferred embodiment in polishing the spiral flute of a tool by means of controlled translational and rotational axes. Especially in the machining of highly magnetic materials, such as HSS steel, the occurring magnetic forces can be too great for robot applications, which were described above by means of FIG. 2. In these cases, it is more advantageous to have the acting forces be absorbed by correspondingly arranged, controllable axes. The rotating magnetic head 33 is driven by a three-phase AC motor 31. This set-up is positioned on a turntable 39, by means of which the angle between the tangent abutting the circumference of the magnetic head 33 and the rotational axis of the tool 35 can be adjusted. The tool 35 to be machined is positioned in a seat and is driven by a servomotor 32, which is controlled by a programmable controller. This set-up is situated on two guides offset 90 degrees to each other, which permit the manual positioning of the tool using the adjustment wheels 38 and 37 in such a manner that the tip of the tool's flute is located in engagement with the circumferential edge of the magnetic head 33. The mentioned manual guides are connected to a guide 34 oriented parallel to the tool axis. The guide 34 is driven by a non-depicted servomotor. Finally, one controls from the programmable controller in such a manner that its translational motion occurs synchronously with the rotation of the tool 35. The servomotor 35 responsible for the tool rotation and the servomotor responsible for the advancing motion of the tool both receive the control pulses from the same programmable controller, whereby a common start time and synchronization of the motions are assured.

While the invention has been illustrated and described in detail in the drawings in the above description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the scope of the invention are desired to be protected. 

1. A machining apparatus to machine a surface in at least one recess of a workpiece, comprising: a circular disk-shaped or frustum-shaped machining body with a symmetrical and rotational axis which is rotatably seated in a bearing and is connected to a machining drive to generate a rotational motion of the machining body about said rotational axis; the machining body having magnets acting outwardly in relation to the rotational axis to retain magnetic or magnetizable abrasive machining powder on a circumferential surface of the machining body; and a workpiece holder for said workpiece positionable relative to the machining body and moveably driven in an advancing or rotational direction or both and which is at least indirectly connected to the bearing of the machining body by means of corresponding positioning media and drives.
 2. A machining apparatus according to claim 1 wherein the machining body is constructed as a magnetic head in which the magnets are formed from a plurality of permanent magnets to retain the machining powder.
 3. A machining apparatus according to claim 1 wherein the workpiece holder has a feed drive and a rotation drive with which a workpiece is to be simultaneously advanced and rotated, the feed drive and the rotation drive being connected to a control unit constructed such that advancing motion and rotational motion of the workpiece are coordinated according to a path of said recess of the workpiece to be machined.
 4. A machining apparatus according to claim 3 wherein the workpiece recess comprises a flute.
 5. A machining apparatus according to claim 1 wherein the recess of the workpiece comprises at least one of a flute or a cutting edge, and wherein the workpiece comprises a twist drill, a milling head, or a reamer.
 6. A machining apparatus to machine a surface in at least one recess of a workpiece, comprising: a circular machining body with a symmetrical rotational axis which is mounted to a rotatable bearing connected to a machining drive to generate a rotational motion of the machining body about said rotational axis; the machining body having a plurality of magnets at a peripheral region to retain abrasive machining powder at a circumferential surface of the machining body; and a workpiece holder for said workpiece positionable relative to the machining body and moveably driven, and the moveable driving being at least indirectly linked to movement of the bearing of the machining body for synchronization thereof.
 7. A machining apparatus to machine a surface in at least one recess of a workpiece, comprising: a circular machining body with a symmetrical rotational axis which is mounted to a rotatable bearing connected to a machining drive to generate a rotational motion of the machining body about said rotational axis; the machining body having a magnet system acting outwardly in relation to the rotational axis to retain abrasive machining powder at a circumferential surface of the machining body; and a workpiece holder for said workpiece positionable relative to the machining body and moveably driven, and the moveable driving being at least indirectly linked to movement of the bearing of the machining body. 